1. Field of the Invention
The present invention relates to a travel device suitable for application to a coaxial two-wheel vehicle including two wheels disposed on the same axis center line, for example. Particularly, the present invention realizes active control of the tilt of a step plate and/or a handle with use of a tilt driving unit so as to maintain the stability while traveling. The present invention is also applicable to a travel device including three or more wheels.
2. Description of Related Art
A coaxial two-wheel vehicle of a related art implements a posture control of a vehicle mainly in a pitch axis direction by detecting the tilt of the vehicle with a use of a plurality of gyroscopes or the like. For example, a related reference U.S. Pat. No. 5,971,091 discloses such a technique.
As another example, there is a device that includes a handle or a step which is constrained to a neutral position by a restoring force of a spring or the like, detects their absolute tilt angle with respect to a gravitational axis or relative tilt angle with respect to a vehicle base and controls each wheel so as to implement a rotating operation according to the detected angle. For example, a related reference Japanese Patent Application No. 2005-117365 filed on Apr. 14, 2005 (Kakinuma, U.S. patent application Ser. No. 11/402,975 filed on Apr. 13, 2006, Pub. No. US 2006/0260857) discloses such a technique.
However, the above patent references do not describe a technique of actively controlling the tilt of at least one of a step plate and a handle to enable stable traveling, which is the main point of the present invention.
As a vehicle that travels with two wheels with a person on board, a coaxial two-wheel vehicle as disclosed in the above related references is known, for example. Specifically, Kakinuma teaches a technique of using a handle or a step that is constrained to a neutral position by a restoring force of a spring or the like, detecting their absolute tilt angle with respect to a gravitational axis or relative tilt angle with respect to a vehicle base and controlling each wheel so as to implement a rotating operation according to the detected angle.
However, if such a vehicle travels straight on a canted road having a lateral inclination in the direction orthogonal to the inclination, it causes the following problems.
Specifically, when using the absolute tilt angle for a rotation control, the neutral position of a handle by a restoring force of a spring or the like is as shown in FIG. 21A. In order to bring the absolute angle of the handle to zero so as to allow the vehicle to move straight, a passenger needs to actively tilt the handle against the spring force to realize the state as shown in FIG. 21B. Such an operation requires enough physical strength and skill to keep tilting the handle against the spring force. Further, if a passenger fails to make an appropriate control of the handle, it can lead to an unintended behavior of the vehicle.
On the other hand, when using the relative tilt angle for a rotation control, the vehicle moves straight in the state as shown in FIG. 21A in which a passenger exerts no force on the handle. However, because the vehicle tilts with respect to the gravitational axis in this state, it is difficult for the passenger to adjust a left-right balance if a lateral inclination of a road is large. Further, when the vehicle rotates on the spot on a slope, the neutral angle of the handle changes with respect to the ground according to a change in the tilt of the vehicle base in the roll axis direction, and therefore a passenger needs to manipulate the vehicle by changing a relative position between his/her own body and the handle.
Further, when a passenger places one foot on a step upon getting on the vehicle having such a structure, the step and the handle tilt due to the load imbalance between right and left on the step as shown in FIG. 21C, and the tilt causes an accidental rotation control. It is thus difficult for a passenger to get on or off the vehicle.